Abstract AdolescentBrainCognitiveDevelopment(ABCD)isthelargestlong-termstudyofbraindevelopmentandchild healthintheUnitedStates.TheABCDResearchConsortiumconsistsof21researchsitesacrossthecountry, aCoordinatingCenter,andaDataAnalysisandInformaticsResourceCenter.Initsfirstfiveyears,under RFA-DA-15-015,ABCDenrolledadiversesampleof11,8789-10yearoldsfromacrosstheconsortium,and willtracktheirbiologicalandbehavioraldevelopmentthroughadolescenceintoyoungadulthood. Allparticipantsreceivedacomprehensivebaselineassessment,includingstate-of-the-artbrainimaging, neuropsychologicaltesting,bioassays,carefulassessmentofsubstanceuse,mentalhealth,physicalhealth, andcultureandenvironment.Asimilardetailedassessmentrecursevery2years.Interimin-personannual interviewsandmid-yeartelephoneormobileappassessmentsproviderefinedtemporalresolutionof developmentalchangesandlifeeventsthatoccurovertimewithminimalburdentoparticipatingyouthand parents.Intensiveeffortsaremadetokeepthevastmajorityofparticipantsinvolvedwiththestudythrough adolescenceandbeyond,andretentionratesthusfarareveryhigh.Neuroimaginghasexpandedour understandingofbraindevelopmentfromchildhoodintoadulthood.Usingthisandothercutting-edge technologies,ABCDcandeterminehowdifferentkindsofyouthexperiences(suchassports,school involvement,extracurricularactivities,videogames,socialmedia,unhealthysleeppatterns,andvaping) interactwitheachotherandwithachild?schangingbiologytoaffectbraindevelopmentandsocial,behavioral, academic,health,andotheroutcomes. Data,securelyandprivatelysharedwiththescientificcommunity,willenableinvestigatorsto:(1)describe individualdevelopmentalpathwaysintermsofneural,cognitive,emotional,andacademicfunctioning,and influencingfactors;?(2)developnationalstandardsofhealthybraindevelopment;?(3)investigatetherolesand interactionofgenesandtheenvironmentondevelopment;?(4)examinehowphysicalactivity,sleep,screen time,sportsinjuries(includingtraumaticbraininjuries),andotherexperiencesinfluencebraindevelopment;?(5) determineandreplicatefactorsthatinfluencementalhealthfromchildhoodtoyoungadulthood;?(6) characterizerelationshipsbetweenmentalhealthandsubstanceuse;?and(7)specifyhowuseofsubstances suchascannabis,alcohol,tobacco,andcaffeineaffectsdevelopmentaloutcomes,andhowneural,cognitive, emotional,andenvironmentalfactorsinfluencetheriskforadolescentsubstanceuse.